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3. (A+B+C)/3=70 (Since its average of the three)
Since there is only one equaltion with a numerical value, thereofre we have to use this eaualtion to find out the value of A, B and C but we can't solve three variables from only one equation. We will substitute values of two other variabe to the third variable in the equation. As we see, all A,B and C-ther are related, we will try to replace 2 of them in eq.3 and make it only one varible.
From eq.1 above, A=B/2
Again, B=C/2, so, We put C/2 above and get, 2A=C/2
So now we see, all variabe can be expressed in terms of C only. So we substitute variables A and B in the main eq. 3 and write in terms of C,
So, A+B+C=70X3 (multiplied both sides with 3)
or, we can write, C/4+C/2+C=210 (from eq. 1 and 2 above)